Strapping machines are well known in the art for securing straps, such as plastic strapping material, around loads. In one configuration, a strapping machine is used to strap compressed loads, such as baled cotton or other textile materials. One such strapping machine is disclosed in commonly assigned patent to Flaum U.S. Pat. No. 7,421,944, which is incorporated herein by reference. Often the loads are large, such that in a typical arrangement, multiple straps are fed, tensioned, and sealed around the load to secure the entire load.
One typical strapping machine includes several separate, but interdependent modular feed and strapping units, each of which includes, among other things, a feed head having a pinch wheel and a drive wheel. A dispenser feeds strap from a strap supply to the feed head. In many configurations, the dispenser is configured to bias the strap directly away from the feed head and toward the dispenser, such as through spring-lock mechanisms as are known in the art.
The strap is directed between the pinch and drive wheel prior to entering a strap chute to encircle the load. The end of the strap is gripped and held between the pinch and drive wheels during the strap feed process. The trailing end of the strap remains gripped between the pinch and drive wheels until the strap is indexed for the next load. Each individual strapping unit operates in a similar manner in conjunction with each other unit so that the strapping occurs simultaneously at each of the several units. In this manner, the strapping operation is carried out in an efficient and time effective operational mode.
While the strap is gripped between the pinch wheel and the drive wheel as it is being fed, a dispenser wheel exerts a retractile force on the strap. Over time, this retractile force can cause the drive and pinch wheels to be pulled out of alignment with each other and mounting elements of each wheel to become loosened or skewed. In addition, the strap can become dislodged from between the wheels. Furthermore, because all the drive wheels in a multi-feed unit strapping machine are typically driven on a common drive shaft of a single motor, if one of the modular feed units requires servicing, all of the modular feed units must be taken out of operation in order to service the unit(s) in need of servicing.
In another type of strapping machine, a strap seal that has been formed is rotated around the load to a more convenient location. In the present example, the motor used to rotate the strap seal around the load, however, is the same motor that drives the drive wheel to feed the strap. Thus, unless the drive wheel is decoupled from the strap, when the motor operates to rotate the strap seal around the load, the motor also feeds excess strap through the strapping machine. Common fixes to this issue have been to add mechanical or electromechanical clutches or other stabilizing mechanisms around the pinch and drive wheels. These mechanisms, however, can be complex, bulky, and heavy, not in keeping with the modular design of the feed unit. In addition, the pinch and drive wheels are still acted upon by forces that could move the wheels out of alignment with each other and cause wear and tear on the pinch and drive wheels themselves.
Accordingly, it would be desirable to have a strap feeder assembly configured to grip and index the strap that prevents or decreases the wear and tear on the pinch and drive wheels of the strap feed head and enables the user to isolate and service one unit without disturbing the remaining units in the assembly. Desirably, such an assembly is in keeping with the modular design of the feed head and is not overly complex, bulky, or heavy. More desirably, such an assembly increases the useful life of the components of the strap feed heads.